COVID-19 vaccine-makers are racing to meet growing demand and address concerns about the effectiveness of their shots against the emerging omicron variant.

Moderna Inc., Pfizer Inc. and BioNTech SE all said they will have data on how their vaccines fare against the new variant over the next two to four weeks, with updated vaccines targeting the new strain also in development.

"Given the large number of mutations, it is highly possible that the efficacy of the vaccine — all of them — is going down," Moderna CEO Stéphane Bancel said in an interview with CNBC. "But we need to wait for the data to know if this is true and how much [it is] going down."

Pfizer started work on an updated vaccine to target the variant Nov. 26, CEO Albert Bourla said, although the executive did suggest that existing shots would still have some effectiveness.

"I don't think the result will be [that] the vaccines don't protect," Bourla told CNBC. "The results could be — which we don't know yet — that the vaccines protect less."

Johnson & Johnson, which is also testing its vaccine against the variant, announced Nov. 27 that the company is expanding a deal with Aspen Pharmacare Holdings Ltd. to allow the South African company to package and sell J&J's shot in that country, where omicron was first identified and is already prevalent.

"Building on our long-term collaboration with scientists on the ground in South Africa and the ongoing real-world effectiveness studies being conducted with the Johnson & Johnson COVID-19 vaccine, we will work together to generate new data on omicron," Mathai Mammen, global head of research and development at J&J's Janssen unit, said in a separate statement. "In parallel, we have begun work to design and develop a new vaccine against omicron and will rapidly progress it into clinical studies if needed."

In addition to South Africa, the virus has been detected in Europe and Canada, and health experts said it has likely already arrived in the U.S. The strain's mutations include those of past COVID-19 virus variants, like delta, as well as new changes that have not yet been characterized, Reynold Panettieri, Rutgers University professor and vice chancellor for translational medicine and science, told S&P Global Market Intelligence.

"The delta variant has nine mutations in the spike proteins, whereas this variant has 32," Panettieri said in an interview. "That could give it a competitive advantage for binding to the receptor of cells in the upper airways and the nose of humans that then become vulnerable to replication of the virus — so it is certainly a variant of concern."

These same mutations that cause the virus to be more transmissible could render existing vaccines less effective, Morgan Stanley analyst Matthew Harrison said in a Nov. 29 note.

"Reduction in vaccine efficacy is highly likely," Harrison said. "The combination of known mutations suggests it should be worse than other variants, but by how much is unclear."

Modified booster shots of existing vaccines will probably be necessary, Harrison said, noting that anecdotal reports suggest even some people recently boosted have been infected.

When it comes to the market, Harrison said mRNA vaccines, like those from Moderna and Pfizer, are likely to benefit most, as well as antibody therapies from AstraZeneca PLC, GlaxoSmithKline PLC-partnered Vir Biotechnology Inc. and newcomer Adagio Therapeutics Inc., which all have a broad profile against the variant, Harrison noted.

Sales of Pfizer and Merck's new COVID-19 at-home pills will also likely increase if the variant produces a rise in infection rates, with Morgan Stanley predicting Nov. 29 that Pfizer's revenue could reach $26 billion in 2022 from its pill alone.

Shares of Moderna have been the most reactive to the omicron variant, as the vaccine maker has been "more outspoken about need and enthusiasm for a new version for 2022 since it makes sense to have the 'newest' one out there to fight COVID," Jefferies analyst Michael Yee said in a Nov. 30 note.

Even before news of the variant had spread, Moderna's Bancel urged vigilance.

"We still are not out of the woods in terms of another variant," the CEO said Nov. 18 at the 2021 Jefferies London Healthcare Conference. "So be careful not to assume we are done with COVID — SARS-CoV-2 is not leaving the planet."

Global role of vaccines

Although vaccines will not directly prevent a mutation from occurring, a reduction in the number of hosts can slow the process, Panettieri said.

"The way that viruses mutate is by having hosts; so as long as there's a host, then the virus will continue to mutate," Panettieri said. "The vaccines themselves decrease the susceptibility of hosts, so by extension, vaccines prevent mutations by preventing the virus from replicating, but it is not a direct effect in preventing the mutation."

Over 74% of the U.S. population aged 5 years and older have received at least one vaccine dose as of Nov. 30, according to the U.S. Centers for Disease Control and Prevention.

"As this variant becomes prevalent in the U.S., there is still a population of people unvaccinated who will be the preferred hosts for this virus," Panettieri said, noting that even vaccinated people remain at risk.

Health experts pointed out that supplying vaccines to other countries is vital to slow infection rates globally and prevent further waves of the disease. In a Nov. 17 white paper, think tank Center for Strategic and International Studies described the U.S. as having a moral responsibility to deliver its millions of surplus vaccine doses to less prosperous countries.

"We've been fortunate to be able to vaccinate a large portion of our population — other countries have not," Panettieri said. "The consequence of that is that there are vulnerable individuals who will be the reservoir for more variants."